Use the “Broadcast a message” tool to communicate with everyone while breakout rooms are in session. This is great to set-up at the start of the breakout rooms as a reminder of the prompt that students are supposed to be discussing and at the end to give a heads-up about time remaining in the rooms.
As the meeting host (or co-host), you can enter breakout rooms to check-in on how students are doing and see if there are any questions (similar to how you would usually walk around a classroom).
Make sure students are aware of the “Ask for help” button that appears at the bottom of the screen which students can use if they get stuck or have a question. (Note that the chat in each room is private to that room.)